Die Casting Services: Published Capability Limits, Not Marketing Adjectives

Ask Every Supplier for Their Numbers

Most die casting services pages describe capability in adjectives. Precision. Excellence. Advanced. State-of-the-art. None of those words tell an engineer whether a part can be made.

The useful question is narrower: what are the actual limits? Smallest part, largest part, thinnest wall, tightest tolerance, smallest viable batch. A supplier who publishes those numbers has decided where the edges are. A supplier who avoids them will discover the edges during your programme.

Below are ours, with the reasoning behind each. Where a limit is soft, we say so. Where a request falls outside it, we say that too — before tooling is cut rather than at first article.

Capability Envelope

Why Each Limit Exists

Clamp Force Is Set by Projected Area

Machines are not selected by part weight. Injection pressure acting on the projected area of the cavity plus runner tries to force the die open, and clamp force must exceed it.

Aluminium needs roughly 2–4 tons per square inch of projected area. A large flat housing with 400 in² projected area requires 800–1,600 tons even if it weighs three kilograms. Conversely a dense compact part weighing eight kilograms may only need 600 tons. Buyers who assume weight determines machine size often misjudge which supplier can run their part.

The 15 g Lower Limit

Very small parts are technically easy but commercially awkward in a single cavity — the shot is mostly runner, cycle time barely changes, and cost per piece stays high. Below 15 g the sensible answer is multi-cavity or family tooling, which changes the tooling conversation. We raise it rather than quoting an inefficient single cavity.

The 25 kg Upper Limit

Two constraints bind together. Ladle capacity limits the metered charge per cycle, and larger shots need proportionally larger clamp force. Beyond 25 kg the economics usually favour gravity or Sand Casting, wherecast metal parts of that scale are routinely produced without extreme tooling investment.

The 1.2 mm Wall — and Why 0.8 mm Claims Need Scrutiny

Aluminium reaches 1.2 mm walls, but only over limited flow distance. A 1.2 mm wall extending 200 mm from the gate will cold-shut: the metal front loses superheat and freezes before the cavity fills.

Wall capability is therefore not a single number but a wall-to-flow-length relationship. Suppliers publishing 0.8 mm for aluminium are usually quoting a laboratory-scale test coupon, not a production part. Zinc genuinely reaches 0.4 mm because its lower melting point and hot chamber injection preserve fluidity far longer.

The 8 mm Upper Wall Limit

Thick sections are not "safe" — they are the hardest thing to cast well. Solidification time scales with the square of section thickness, so an 8 mm wall takes roughly four times as long to freeze as a 4 mm wall. The gate freezes first, cutting off feed, and the interior shrinks into porosity.

Where a design genuinely needs mass, we core it out and add ribs. Where it needs 8 mm for thread engagement, we accept it locally and place a squeeze pin.

Casting Processes and Alloys

Cold Chamber — Aluminium

The shot sleeve sits outside the melt. An automatic ladler transfers a metered charge each cycle, then a hydraulic plunger injects at 700–1,200 bar, filling in milliseconds.

Two clarifications worth making, because they are frequently stated incorrectly:

The transfer is automated, not manual. Modern Aluminum Die Casting cells use servo ladlers delivering a repeatable charge weight every cycle. Manual pouring cannot hold the shot-to-shot consistency that SPC requires.

Magnesium runs cold chamber, not hot chamber. Some capability pages group magnesium with zinc because both melt below aluminium. But magnesium's reactivity and the protective cover gas system it requires place it firmly in cold chamber practice.

Hot Chamber — Zinc

The gooseneck injection system sits submerged in the zinc pot. At 385–400°C, submerged hardware survives, and eliminating the ladling step removes several seconds per cycle. This is why zinc casting achieves cycle times and tool life that aluminium cannot approach.

Alloy Range

Two constraints we flag at quotation. A380 does not anodise bright — its 3–4% copper produces a mottled dark grey film, so bright anodised parts need A360 or A413 specified before tooling. And 6061 cannot be die cast: at 0.4–0.8% silicon it has poor fluidity and hot-tears in a steel die, so that drawing needs CNC machining from billet or aluminum fabrication from extrusion.

What the Tolerance Numbers Actually Mean

Published tolerance figures mislead more buyers than any other specification, because three different numbers get quoted as though they were one.

±0.10 mm per 25 mm applies within a single die half. Two features formed by the same steel block hold this well.

±0.25 mm applies across the parting line. Features split between the fixed and moving halves inherit clamp repeatability on top of cavity accuracy. If a critical dimension spans the parting line, either move the split at DFM or machine the feature afterwards.

±0.02 mm is a machining tolerance. Any supplier quoting ±0.01 mm as an as-cast capability is quoting a secondary operation without saying so.

The practical consequence: apply tight tolerances only to critical-to-function features. A drawing carrying ±0.05 mm on every dimension forces machining of every surface, and can double the piece price of an otherwise straightforward die cast housing.

Machining and Finishing

Precision machining — bores, threaded ports, sealing faces and datums to ±0.02 mm on 3, 4 and 5-axis centres. Threads are always machined rather than cast; cast threads rarely achieve the surface finish reliable sealing requires.

One machining consideration specific to castings: the as-cast skin is the strongest material in the part. Rapid die contact produces a dense fine-grained layer roughly 0.3–0.5 mm deep. Machining it away removes the best material and exposes the more porous core. Where a surface must be machined, we minimise stock removal rather than facing off 2 mm for convenience.

Surface finishing:

Two specification points that cause assembly failures:

Anodising insulates; chemical film conducts. Where a housing relies on a bolted joint for chassis ground or wall continuity for EMI shielding, full anodising breaks that path. We mask grounding pads or apply chemical film only, recorded as a defined zone with a stated resistance limit.

Coating consumes clearance. Anodising grows roughly half into the substrate and half outward, so 25 µm hard anodise reduces a bore by around 25 µm. Powder coat at 60–120 µm builds unevenly on edges. State on the drawing whether dimensions apply before or after coating.

Metal fabrication — laser cutting, CNC press brake forming, TIG and MIG welding. Many assemblies are best built as hybrids: a cast body carrying complex sealed geometry with custom metal fabrication brackets attached, which frequently removes side actions from the die. Running both in-house means tolerance stack-up is engineered by one team. For low-volume structural fabrication — frames, chassis, panels — no tooling is required and parts ship in one to three weeks.

Product Range

Alt text: Die cast components showing as-cast aluminium finned enclosure housing, bead blasted gearbox cover, anodised heat sink, powder coated electronics housing, polished zinc handle and machined aluminium valve body

Aluminium — enclosures, heat sinks, gear casings, valve bodies, motor housings, brackets, lighting housings.

Zinc — locks, hinges, connectors, gauging components, decorative hardware, precision mechanisms.

Fluid handling — manifolds and bodies in A413 for pressure tightness. For pipe fittings manufacturer requirements, threads are machined post-cast and radiographic acceptance specified per ASTM E505 with a drawing zone map.

Quality Control

Certification: ISO 9001:2015 · IATF 16949. PPAP Level 3 including FMEA, control plan, MSA and capability study.

Porosity control. Gas porosity — rounded dispersed pores from entrained air and lubricant vapour — is controlled by vacuum assist, evacuating below 50 mbar before injection and cutting gas porosity 60–80%. Shrinkage porosity — irregular voids where the gate freezes before heavy sections solidify — is controlled by local squeeze pins or eliminated at DFM by coring out thermal mass. Pressure-tight parts need both.

How Projects Run

1. RFQ and DFM. Send 3D geometry and a 2D drawing with tolerances and finish. DFM feedback returns within 48 hours covering wall thickness, draft, radii, boss proportions, parting line, gate location and required side actions. A quotation with no DFM comment means the supplier has priced the problems in and stayed silent.
2. Simulation. Solidification analysis runs before steel is cut, predicting fill sequence, air entrapment and last-to-freeze regions. Each avoided cavity modification saves three to four weeks.
3. Tooling. H13 steel, vacuum heat treated to 44–48 HRC, nitrided. Built modular with replaceable cavity blocks, gate inserts and core pins so wear items can be changed without rebuilding the tool.
4. T1 samples. Full dimensional report with actual values, plus samples that have been through the complete machining route — residual stress relieves during metal removal, so a casting that measures correctly before machining may not after.
5. Production. Process parameters locked and monitored. Any change to shot profile, alloy source or thermal setup is formally notified, not made silently.

Frequently Asked Questions